Loss Analysis of a Direct-Injection Hydrogen Combustion Engine 2018-01-1686

In the discussion on the reduction or complete avoidance of CO₂-emissions and other pollutants in the transport sector, hydrogen as a carbon-free fuel, is an alternative to conventional fuels. The use of hydrogen in modern internal combustion engines offers a fast and cost-effective opportunity of decarbonisation of the transport sector.

The utilisation of hydrogen as fuel in internal combustion engine systems is more challenging than using conventional fuels. Hydrogen is highly flammable, which affects the requirements of the ignition system and the design of the combustion chamber. In addition, due to the gaseous state of H₂ the question, how the fuel should be delivered to the combustion chamber is of high importance by means of engine performance. There are two fundamentally different concepts for hydrogen injection. Hydrogen can be injected by a multi-point injection into intake manifold by external mixture-formation (MPI) or directly into the combustion chamber (DI). When external mixture-formation is used, backfiring due to pre-ignition caused by local hotspots, has to be avoided. Furthermore, fuel backflows can occur as a result of pressure fluctuations which lead to inhomogeneous fuel distribution in the combustion chambers. Due to its low density, hydrogen expands strongly when it is injected in the intake manifold, resulting in fresh air displacement by hydrogen. Hereby effective the delivery rate of the internal combustion engine is significantly lowered.

By using H₂ direct injection, the effect on the filling losses above mentioned are avoided. Due to the specific properties of hydrogen, the fuel preparation is quite complex. According to [1], the performance advantage by using a direct injection of H₂ compared to a gasoline engine with port injection is 15%. In order to exploit the entire efficiency potential, it is eminent that the H₂ injection takes place directly into the combustion chamber. Injection timing could be identified “as dominating influence factor [for] the combustion process and the resulting emissions” [2]. So for an optimized engine performance of an H₂-DI engine, injection timing and injection strategy are crucial. The main focus of this study is an analysis of thermodynamic and mechanic losses of the H₂-DI engine process to compare the efficiencies of DI with H₂-MPI and Diesel compression-ignition (CI)-operation. For this purpose, a one-dimensional H₂-DI simulation model was developed. The model is based on measured data of a H₂-MPI engine which was derived from a commercial Diesel engine.